Fazlur Khan and Bruce Graham

The Sears Tower

Chief engineerFazlur Khan and SOM architect BruceGraham decided that the Sears Towerwould have nine tubes bundledtogether. Each tube would be a 75foot (23 m) square. All the tubeswould rise to a height of forty-ninestories. Three tubes would end at thisheight. The rest would end at higherfloors. Only two would rise to the fullheight of ninety-five stories.With this design, the floor spacedecreases as the tower rises. Searscould use the larger lower floors.The company could rent the smallerupper floors until it needed them. Theoutside open spaces created wheretubes ended are called setbacks. Thesetbacks gave the tower a unique look.When the steel tubes and trusses werefinished, the building was covered in blackaluminum and dark-tinted windows. This typeof smooth exterior is called a curtain wall.Curtain walls add to a skyscraper’s upright look.